5.4.2 PythonDebug

Normally, the traceback output resulting from uncaught Python errors
is sent to the error log. With PythonDebug On directive specified, the
output will be sent to the client (as well as the log), except when
the error is IOError while writing, in which case it will go
to the error log.

This directive is very useful during the development process. It is
recommended that you do not use it production environment as it may
reveal to the client unintended, possibly sensitive security
information.